14.2. "configparser" --- Configuration file parser
**************************************************

**Source code:** Lib/configparser.py

======================================================================

This module provides the "ConfigParser" class which implements a basic
configuration language which provides a structure similar to what's
found in Microsoft Windows INI files.  You can use this to write
Python programs which can be customized by end users easily.

注解: This library does *not* interpret or write the value-type
  prefixes used in the Windows Registry extended version of INI
  syntax.

参见:

  Module "shlex"
     Support for creating Unix shell-like mini-languages which can be
     used as an alternate format for application configuration files.

  Module "json"
     The json module implements a subset of JavaScript syntax which
     can also be used for this purpose.


14.2.1. Quick Start
===================

Let's take a very basic configuration file that looks like this:

   [DEFAULT]
   ServerAliveInterval = 45
   Compression = yes
   CompressionLevel = 9
   ForwardX11 = yes

   [bitbucket.org]
   User = hg

   [topsecret.server.com]
   Port = 50022
   ForwardX11 = no

The structure of INI files is described in the following section.
Essentially, the file consists of sections, each of which contains
keys with values. "configparser" classes can read and write such
files.  Let's start by creating the above configuration file
programmatically.

   >>> import configparser
   >>> config = configparser.ConfigParser()
   >>> config['DEFAULT'] = {'ServerAliveInterval': '45',
   ...                      'Compression': 'yes',
   ...                      'CompressionLevel': '9'}
   >>> config['bitbucket.org'] = {}
   >>> config['bitbucket.org']['User'] = 'hg'
   >>> config['topsecret.server.com'] = {}
   >>> topsecret = config['topsecret.server.com']
   >>> topsecret['Port'] = '50022'     # mutates the parser
   >>> topsecret['ForwardX11'] = 'no'  # same here
   >>> config['DEFAULT']['ForwardX11'] = 'yes'
   >>> with open('example.ini', 'w') as configfile:
   ...   config.write(configfile)
   ...

As you can see, we can treat a config parser much like a dictionary.
There are differences, outlined later, but the behavior is very close
to what you would expect from a dictionary.

Now that we have created and saved a configuration file, let's read it
back and explore the data it holds.

   >>> import configparser
   >>> config = configparser.ConfigParser()
   >>> config.sections()
   []
   >>> config.read('example.ini')
   ['example.ini']
   >>> config.sections()
   ['bitbucket.org', 'topsecret.server.com']
   >>> 'bitbucket.org' in config
   True
   >>> 'bytebong.com' in config
   False
   >>> config['bitbucket.org']['User']
   'hg'
   >>> config['DEFAULT']['Compression']
   'yes'
   >>> topsecret = config['topsecret.server.com']
   >>> topsecret['ForwardX11']
   'no'
   >>> topsecret['Port']
   '50022'
   >>> for key in config['bitbucket.org']: print(key)
   ...
   user
   compressionlevel
   serveraliveinterval
   compression
   forwardx11
   >>> config['bitbucket.org']['ForwardX11']
   'yes'

As we can see above, the API is pretty straightforward.  The only bit
of magic involves the "DEFAULT" section which provides default values
for all other sections [1].  Note also that keys in sections are case-
insensitive and stored in lowercase [1].


14.2.2. Supported Datatypes
===========================

Config parsers do not guess datatypes of values in configuration
files, always storing them internally as strings.  This means that if
you need other datatypes, you should convert on your own:

   >>> int(topsecret['Port'])
   50022
   >>> float(topsecret['CompressionLevel'])
   9.0

Since this task is so common, config parsers provide a range of handy
getter methods to handle integers, floats and booleans.  The last one
is the most interesting because simply passing the value to "bool()"
would do no good since "bool('False')" is still "True".  This is why
config parsers also provide "getboolean()".  This method is case-
insensitive and recognizes Boolean values from "'yes'"/"'no'",
"'on'"/"'off'", "'true'"/"'false'" and "'1'"/"'0'" [1].  For example:

   >>> topsecret.getboolean('ForwardX11')
   False
   >>> config['bitbucket.org'].getboolean('ForwardX11')
   True
   >>> config.getboolean('bitbucket.org', 'Compression')
   True

Apart from "getboolean()", config parsers also provide equivalent
"getint()" and "getfloat()" methods.  You can register your own
converters and customize the provided ones. [1]


14.2.3. Fallback Values
=======================

As with a dictionary, you can use a section's "get()" method to
provide fallback values:

   >>> topsecret.get('Port')
   '50022'
   >>> topsecret.get('CompressionLevel')
   '9'
   >>> topsecret.get('Cipher')
   >>> topsecret.get('Cipher', '3des-cbc')
   '3des-cbc'

Please note that default values have precedence over fallback values.
For instance, in our example the "'CompressionLevel'" key was
specified only in the "'DEFAULT'" section.  If we try to get it from
the section "'topsecret.server.com'", we will always get the default,
even if we specify a fallback:

   >>> topsecret.get('CompressionLevel', '3')
   '9'

One more thing to be aware of is that the parser-level "get()" method
provides a custom, more complex interface, maintained for backwards
compatibility.  When using this method, a fallback value can be
provided via the "fallback" keyword-only argument:

   >>> config.get('bitbucket.org', 'monster',
   ...            fallback='No such things as monsters')
   'No such things as monsters'

The same "fallback" argument can be used with the "getint()",
"getfloat()" and "getboolean()" methods, for example:

   >>> 'BatchMode' in topsecret
   False
   >>> topsecret.getboolean('BatchMode', fallback=True)
   True
   >>> config['DEFAULT']['BatchMode'] = 'no'
   >>> topsecret.getboolean('BatchMode', fallback=True)
   False


14.2.4. Supported INI File Structure
====================================

A configuration file consists of sections, each led by a "[section]"
header, followed by key/value entries separated by a specific string
("=" or ":" by default [1]).  By default, section names are case
sensitive but keys are not [1].  Leading and trailing whitespace is
removed from keys and values. Values can be omitted, in which case the
key/value delimiter may also be left out.  Values can also span
multiple lines, as long as they are indented deeper than the first
line of the value.  Depending on the parser's mode, blank lines may be
treated as parts of multiline values or ignored.

Configuration files may include comments, prefixed by specific
characters ("#" and ";" by default [1]).  Comments may appear on their
own on an otherwise empty line, possibly indented. [1]

例如:

   [Simple Values]
   key=value
   spaces in keys=allowed
   spaces in values=allowed as well
   spaces around the delimiter = obviously
   you can also use : to delimit keys from values

   [All Values Are Strings]
   values like this: 1000000
   or this: 3.14159265359
   are they treated as numbers? : no
   integers, floats and booleans are held as: strings
   can use the API to get converted values directly: true

   [Multiline Values]
   chorus: I'm a lumberjack, and I'm okay
       I sleep all night and I work all day

   [No Values]
   key_without_value
   empty string value here =

   [You can use comments]
   # like this
   ; or this

   # By default only in an empty line.
   # Inline comments can be harmful because they prevent users
   # from using the delimiting characters as parts of values.
   # That being said, this can be customized.

       [Sections Can Be Indented]
           can_values_be_as_well = True
           does_that_mean_anything_special = False
           purpose = formatting for readability
           multiline_values = are
               handled just fine as
               long as they are indented
               deeper than the first line
               of a value
           # Did I mention we can indent comments, too?


14.2.5. Interpolation of values
===============================

On top of the core functionality, "ConfigParser" supports
interpolation.  This means values can be preprocessed before returning
them from "get()" calls.

class configparser.BasicInterpolation

   The default implementation used by "ConfigParser".  It enables
   values to contain format strings which refer to other values in the
   same section, or values in the special default section [1].
   Additional default values can be provided on initialization.

   例如:

      [Paths]
      home_dir: /Users
      my_dir: %(home_dir)s/lumberjack
      my_pictures: %(my_dir)s/Pictures

   In the example above, "ConfigParser" with *interpolation* set to
   "BasicInterpolation()" would resolve "%(home_dir)s" to the value of
   "home_dir" ("/Users" in this case).  "%(my_dir)s" in effect would
   resolve to "/Users/lumberjack".  All interpolations are done on
   demand so keys used in the chain of references do not have to be
   specified in any specific order in the configuration file.

   With "interpolation" set to "None", the parser would simply return
   "%(my_dir)s/Pictures" as the value of "my_pictures" and
   "%(home_dir)s/lumberjack" as the value of "my_dir".

class configparser.ExtendedInterpolation

   An alternative handler for interpolation which implements a more
   advanced syntax, used for instance in "zc.buildout".  Extended
   interpolation is using "${section:option}" to denote a value from a
   foreign section. Interpolation can span multiple levels.  For
   convenience, if the "section:" part is omitted, interpolation
   defaults to the current section (and possibly the default values
   from the special section).

   For example, the configuration specified above with basic
   interpolation, would look like this with extended interpolation:

      [Paths]
      home_dir: /Users
      my_dir: ${home_dir}/lumberjack
      my_pictures: ${my_dir}/Pictures

   Values from other sections can be fetched as well:

      [Common]
      home_dir: /Users
      library_dir: /Library
      system_dir: /System
      macports_dir: /opt/local

      [Frameworks]
      Python: 3.2
      path: ${Common:system_dir}/Library/Frameworks/

      [Arthur]
      nickname: Two Sheds
      last_name: Jackson
      my_dir: ${Common:home_dir}/twosheds
      my_pictures: ${my_dir}/Pictures
      python_dir: ${Frameworks:path}/Python/Versions/${Frameworks:Python}


14.2.6. Mapping Protocol Access
===============================

3.2 新版功能.

Mapping protocol access is a generic name for functionality that
enables using custom objects as if they were dictionaries.  In case of
"configparser", the mapping interface implementation is using the
"parser['section']['option']" notation.

"parser['section']" in particular returns a proxy for the section's
data in the parser.  This means that the values are not copied but
they are taken from the original parser on demand.  What's even more
important is that when values are changed on a section proxy, they are
actually mutated in the original parser.

"configparser" objects behave as close to actual dictionaries as
possible. The mapping interface is complete and adheres to the
"MutableMapping" ABC. However, there are a few differences that should
be taken into account:

* By default, all keys in sections are accessible in a case-
  insensitive manner [1].  E.g. "for option in parser["section"]"
  yields only "optionxform"'ed option key names.  This means
  lowercased keys by default.  At the same time, for a section that
  holds the key "'a'", both expressions return "True":

     "a" in parser["section"]
     "A" in parser["section"]

* All sections include "DEFAULTSECT" values as well which means that
  ".clear()" on a section may not leave the section visibly empty.
  This is because default values cannot be deleted from the section
  (because technically they are not there).  If they are overridden in
  the section, deleting causes the default value to be visible again.
  Trying to delete a default value causes a "KeyError".

* "DEFAULTSECT" cannot be removed from the parser:

  * trying to delete it raises "ValueError",

  * "parser.clear()" leaves it intact,

  * "parser.popitem()" never returns it.

* "parser.get(section, option, **kwargs)" - the second argument is
  **not** a fallback value.  Note however that the section-level
  "get()" methods are compatible both with the mapping protocol and
  the classic configparser API.

* "parser.items()" is compatible with the mapping protocol (returns
  a list of *section_name*, *section_proxy* pairs including the
  DEFAULTSECT).  However, this method can also be invoked with
  arguments: "parser.items(section, raw, vars)".  The latter call
  returns a list of *option*, *value* pairs for a specified "section",
  with all interpolations expanded (unless "raw=True" is provided).

The mapping protocol is implemented on top of the existing legacy API
so that subclasses overriding the original interface still should have
mappings working as expected.


14.2.7. Customizing Parser Behaviour
====================================

There are nearly as many INI format variants as there are applications
using it. "configparser" goes a long way to provide support for the
largest sensible set of INI styles available.  The default
functionality is mainly dictated by historical background and it's
very likely that you will want to customize some of the features.

The most common way to change the way a specific config parser works
is to use the "__init__()" options:

* *defaults*, default value: "None"

  This option accepts a dictionary of key-value pairs which will be
  initially put in the "DEFAULT" section.  This makes for an elegant
  way to support concise configuration files that don't specify values
  which are the same as the documented default.

  Hint: if you want to specify default values for a specific section,
  use "read_dict()" before you read the actual file.

* *dict_type*, default value: "collections.OrderedDict"

  This option has a major impact on how the mapping protocol will
  behave and how the written configuration files look.  With the
  default ordered dictionary, every section is stored in the order
  they were added to the parser.  Same goes for options within
  sections.

  An alternative dictionary type can be used for example to sort
  sections and options on write-back.  You can also use a regular
  dictionary for performance reasons.

  Please note: there are ways to add a set of key-value pairs in a
  single operation.  When you use a regular dictionary in those
  operations, the order of the keys may be random.  For example:

     >>> parser = configparser.ConfigParser()
     >>> parser.read_dict({'section1': {'key1': 'value1',
     ...                                'key2': 'value2',
     ...                                'key3': 'value3'},
     ...                   'section2': {'keyA': 'valueA',
     ...                                'keyB': 'valueB',
     ...                                'keyC': 'valueC'},
     ...                   'section3': {'foo': 'x',
     ...                                'bar': 'y',
     ...                                'baz': 'z'}
     ... })
     >>> parser.sections()
     ['section3', 'section2', 'section1']
     >>> [option for option in parser['section3']]
     ['baz', 'foo', 'bar']

  In these operations you need to use an ordered dictionary as well:

     >>> from collections import OrderedDict
     >>> parser = configparser.ConfigParser()
     >>> parser.read_dict(
     ...   OrderedDict((
     ...     ('s1',
     ...      OrderedDict((
     ...        ('1', '2'),
     ...        ('3', '4'),
     ...        ('5', '6'),
     ...      ))
     ...     ),
     ...     ('s2',
     ...      OrderedDict((
     ...        ('a', 'b'),
     ...        ('c', 'd'),
     ...        ('e', 'f'),
     ...      ))
     ...     ),
     ...   ))
     ... )
     >>> parser.sections()
     ['s1', 's2']
     >>> [option for option in parser['s1']]
     ['1', '3', '5']
     >>> [option for option in parser['s2'].values()]
     ['b', 'd', 'f']

* *allow_no_value*, default value: "False"

  Some configuration files are known to include settings without
  values, but which otherwise conform to the syntax supported by
  "configparser".  The *allow_no_value* parameter to the constructor
  can be used to indicate that such values should be accepted:

     >>> import configparser

     >>> sample_config = """
     ... [mysqld]
     ...   user = mysql
     ...   pid-file = /var/run/mysqld/mysqld.pid
     ...   skip-external-locking
     ...   old_passwords = 1
     ...   skip-bdb
     ...   # we don't need ACID today
     ...   skip-innodb
     ... """
     >>> config = configparser.ConfigParser(allow_no_value=True)
     >>> config.read_string(sample_config)

     >>> # Settings with values are treated as before:
     >>> config["mysqld"]["user"]
     'mysql'

     >>> # Settings without values provide None:
     >>> config["mysqld"]["skip-bdb"]

     >>> # Settings which aren't specified still raise an error:
     >>> config["mysqld"]["does-not-exist"]
     Traceback (most recent call last):
       ...
     KeyError: 'does-not-exist'

* *delimiters*, default value: "('=', ':')"

  Delimiters are substrings that delimit keys from values within a
  section. The first occurrence of a delimiting substring on a line is
  considered a delimiter.  This means values (but not keys) can
  contain the delimiters.

  See also the *space_around_delimiters* argument to
  "ConfigParser.write()".

* *comment_prefixes*, default value: "('#', ';')"

* *inline_comment_prefixes*, default value: "None"

  Comment prefixes are strings that indicate the start of a valid
  comment within a config file. *comment_prefixes* are used only on
  otherwise empty lines (optionally indented) whereas
  *inline_comment_prefixes* can be used after every valid value (e.g.
  section names, options and empty lines as well).  By default inline
  comments are disabled and "'#'" and "';'" are used as prefixes for
  whole line comments.

  在 3.2 版更改: In previous versions of "configparser" behaviour
  matched "comment_prefixes=('#',';')" and
  "inline_comment_prefixes=(';',)".

  Please note that config parsers don't support escaping of comment
  prefixes so using *inline_comment_prefixes* may prevent users from
  specifying option values with characters used as comment prefixes.
  When in doubt, avoid setting *inline_comment_prefixes*.  In any
  circumstances, the only way of storing comment prefix characters at
  the beginning of a line in multiline values is to interpolate the
  prefix, for example:

     >>> from configparser import ConfigParser, ExtendedInterpolation
     >>> parser = ConfigParser(interpolation=ExtendedInterpolation())
     >>> # the default BasicInterpolation could be used as well
     >>> parser.read_string("""
     ... [DEFAULT]
     ... hash = #
     ...
     ... [hashes]
     ... shebang =
     ...   ${hash}!/usr/bin/env python
     ...   ${hash} -*- coding: utf-8 -*-
     ...
     ... extensions =
     ...   enabled_extension
     ...   another_extension
     ...   #disabled_by_comment
     ...   yet_another_extension
     ...
     ... interpolation not necessary = if # is not at line start
     ... even in multiline values = line #1
     ...   line #2
     ...   line #3
     ... """)
     >>> print(parser['hashes']['shebang'])

     #!/usr/bin/env python
     # -*- coding: utf-8 -*-
     >>> print(parser['hashes']['extensions'])

     enabled_extension
     another_extension
     yet_another_extension
     >>> print(parser['hashes']['interpolation not necessary'])
     if # is not at line start
     >>> print(parser['hashes']['even in multiline values'])
     line #1
     line #2
     line #3

* *strict*, default value: "True"

  When set to "True", the parser will not allow for any section or
  option duplicates while reading from a single source (using
  "read_file()", "read_string()" or "read_dict()").  It is recommended
  to use strict parsers in new applications.

  在 3.2 版更改: In previous versions of "configparser" behaviour
  matched "strict=False".

* *empty_lines_in_values*, default value: "True"

  In config parsers, values can span multiple lines as long as they
  are indented more than the key that holds them.  By default parsers
  also let empty lines to be parts of values.  At the same time, keys
  can be arbitrarily indented themselves to improve readability.  In
  consequence, when configuration files get big and complex, it is
  easy for the user to lose track of the file structure.  Take for
  instance:

     [Section]
     key = multiline
       value with a gotcha

      this = is still a part of the multiline value of 'key'

  This can be especially problematic for the user to see if she's
  using a proportional font to edit the file.  That is why when your
  application does not need values with empty lines, you should
  consider disallowing them.  This will make empty lines split keys
  every time.  In the example above, it would produce two keys, "key"
  and "this".

* *default_section*, default value: "configparser.DEFAULTSECT" (that
  is: ""DEFAULT"")

  The convention of allowing a special section of default values for
  other sections or interpolation purposes is a powerful concept of
  this library, letting users create complex declarative
  configurations.  This section is normally called ""DEFAULT"" but
  this can be customized to point to any other valid section name.
  Some typical values include: ""general"" or ""common"".  The name
  provided is used for recognizing default sections when reading from
  any source and is used when writing configuration back to a file.
  Its current value can be retrieved using the
  "parser_instance.default_section" attribute and may be modified at
  runtime (i.e. to convert files from one format to another).

* *interpolation*, default value: "configparser.BasicInterpolation"

  Interpolation behaviour may be customized by providing a custom
  handler through the *interpolation* argument. "None" can be used to
  turn off interpolation completely, "ExtendedInterpolation()"
  provides a more advanced variant inspired by "zc.buildout".  More on
  the subject in the dedicated documentation section.
  "RawConfigParser" has a default value of "None".

* *converters*, default value: not set

  Config parsers provide option value getters that perform type
  conversion.  By default "getint()", "getfloat()", and "getboolean()"
  are implemented.  Should other getters be desirable, users may
  define them in a subclass or pass a dictionary where each key is a
  name of the converter and each value is a callable implementing said
  conversion.  For instance, passing "{'decimal': decimal.Decimal}"
  would add "getdecimal()" on both the parser object and all section
  proxies.  In other words, it will be possible to write both
  "parser_instance.getdecimal('section', 'key', fallback=0)" and
  "parser_instance['section'].getdecimal('key', 0)".

  If the converter needs to access the state of the parser, it can be
  implemented as a method on a config parser subclass.  If the name of
  this method starts with "get", it will be available on all section
  proxies, in the dict-compatible form (see the "getdecimal()" example
  above).

More advanced customization may be achieved by overriding default
values of these parser attributes.  The defaults are defined on the
classes, so they may be overridden by subclasses or by attribute
assignment.

ConfigParser.BOOLEAN_STATES

   By default when using "getboolean()", config parsers consider the
   following values "True": "'1'", "'yes'", "'true'", "'on'" and the
   following values "False": "'0'", "'no'", "'false'", "'off'".  You
   can override this by specifying a custom dictionary of strings and
   their Boolean outcomes. For example:

      >>> custom = configparser.ConfigParser()
      >>> custom['section1'] = {'funky': 'nope'}
      >>> custom['section1'].getboolean('funky')
      Traceback (most recent call last):
      ...
      ValueError: Not a boolean: nope
      >>> custom.BOOLEAN_STATES = {'sure': True, 'nope': False}
      >>> custom['section1'].getboolean('funky')
      False

   Other typical Boolean pairs include "accept"/"reject" or
   "enabled"/"disabled".

ConfigParser.optionxform(option)

   This method transforms option names on every read, get, or set
   operation.  The default converts the name to lowercase.  This also
   means that when a configuration file gets written, all keys will be
   lowercase.  Override this method if that's unsuitable. For example:

      >>> config = """
      ... [Section1]
      ... Key = Value
      ...
      ... [Section2]
      ... AnotherKey = Value
      ... """
      >>> typical = configparser.ConfigParser()
      >>> typical.read_string(config)
      >>> list(typical['Section1'].keys())
      ['key']
      >>> list(typical['Section2'].keys())
      ['anotherkey']
      >>> custom = configparser.RawConfigParser()
      >>> custom.optionxform = lambda option: option
      >>> custom.read_string(config)
      >>> list(custom['Section1'].keys())
      ['Key']
      >>> list(custom['Section2'].keys())
      ['AnotherKey']

ConfigParser.SECTCRE

   A compiled regular expression used to parse section headers.  The
   default matches "[section]" to the name ""section"".  Whitespace is
   considered part of the section name, thus "[  larch  ]" will be
   read as a section of name ""  larch  "".  Override this attribute
   if that's unsuitable.  For example:

      >>> config = """
      ... [Section 1]
      ... option = value
      ...
      ... [  Section 2  ]
      ... another = val
      ... """
      >>> typical = ConfigParser()
      >>> typical.read_string(config)
      >>> typical.sections()
      ['Section 1', '  Section 2  ']
      >>> custom = ConfigParser()
      >>> custom.SECTCRE = re.compile(r"\[ *(?P<header>[^]]+?) *\]")
      >>> custom.read_string(config)
      >>> custom.sections()
      ['Section 1', 'Section 2']

   注解: While ConfigParser objects also use an "OPTCRE" attribute
     for recognizing option lines, it's not recommended to override it
     because that would interfere with constructor options
     *allow_no_value* and *delimiters*.


14.2.8. Legacy API Examples
===========================

Mainly because of backwards compatibility concerns, "configparser"
provides also a legacy API with explicit "get"/"set" methods.  While
there are valid use cases for the methods outlined below, mapping
protocol access is preferred for new projects.  The legacy API is at
times more advanced, low-level and downright counterintuitive.

An example of writing to a configuration file:

   import configparser

   config = configparser.RawConfigParser()

   # Please note that using RawConfigParser's set functions, you can assign
   # non-string values to keys internally, but will receive an error when
   # attempting to write to a file or when you get it in non-raw mode. Setting
   # values using the mapping protocol or ConfigParser's set() does not allow
   # such assignments to take place.
   config.add_section('Section1')
   config.set('Section1', 'an_int', '15')
   config.set('Section1', 'a_bool', 'true')
   config.set('Section1', 'a_float', '3.1415')
   config.set('Section1', 'baz', 'fun')
   config.set('Section1', 'bar', 'Python')
   config.set('Section1', 'foo', '%(bar)s is %(baz)s!')

   # Writing our configuration file to 'example.cfg'
   with open('example.cfg', 'w') as configfile:
       config.write(configfile)

An example of reading the configuration file again:

   import configparser

   config = configparser.RawConfigParser()
   config.read('example.cfg')

   # getfloat() raises an exception if the value is not a float
   # getint() and getboolean() also do this for their respective types
   a_float = config.getfloat('Section1', 'a_float')
   an_int = config.getint('Section1', 'an_int')
   print(a_float + an_int)

   # Notice that the next output does not interpolate '%(bar)s' or '%(baz)s'.
   # This is because we are using a RawConfigParser().
   if config.getboolean('Section1', 'a_bool'):
       print(config.get('Section1', 'foo'))

To get interpolation, use "ConfigParser":

   import configparser

   cfg = configparser.ConfigParser()
   cfg.read('example.cfg')

   # Set the optional *raw* argument of get() to True if you wish to disable
   # interpolation in a single get operation.
   print(cfg.get('Section1', 'foo', raw=False))  # -> "Python is fun!"
   print(cfg.get('Section1', 'foo', raw=True))   # -> "%(bar)s is %(baz)s!"

   # The optional *vars* argument is a dict with members that will take
   # precedence in interpolation.
   print(cfg.get('Section1', 'foo', vars={'bar': 'Documentation',
                                          'baz': 'evil'}))

   # The optional *fallback* argument can be used to provide a fallback value
   print(cfg.get('Section1', 'foo'))
         # -> "Python is fun!"

   print(cfg.get('Section1', 'foo', fallback='Monty is not.'))
         # -> "Python is fun!"

   print(cfg.get('Section1', 'monster', fallback='No such things as monsters.'))
         # -> "No such things as monsters."

   # A bare print(cfg.get('Section1', 'monster')) would raise NoOptionError
   # but we can also use:

   print(cfg.get('Section1', 'monster', fallback=None))
         # -> None

Default values are available in both types of ConfigParsers.  They are
used in interpolation if an option used is not defined elsewhere.

   import configparser

   # New instance with 'bar' and 'baz' defaulting to 'Life' and 'hard' each
   config = configparser.ConfigParser({'bar': 'Life', 'baz': 'hard'})
   config.read('example.cfg')

   print(config.get('Section1', 'foo'))     # -> "Python is fun!"
   config.remove_option('Section1', 'bar')
   config.remove_option('Section1', 'baz')
   print(config.get('Section1', 'foo'))     # -> "Life is hard!"


14.2.9. ConfigParser Objects
============================

class configparser.ConfigParser(defaults=None, dict_type=collections.OrderedDict, allow_no_value=False, delimiters=('=', ':'), comment_prefixes=('#', ';'), inline_comment_prefixes=None, strict=True, empty_lines_in_values=True, default_section=configparser.DEFAULTSECT, interpolation=BasicInterpolation(), converters={})

   The main configuration parser.  When *defaults* is given, it is
   initialized into the dictionary of intrinsic defaults.  When
   *dict_type* is given, it will be used to create the dictionary
   objects for the list of sections, for the options within a section,
   and for the default values.

   When *delimiters* is given, it is used as the set of substrings
   that divide keys from values.  When *comment_prefixes* is given, it
   will be used as the set of substrings that prefix comments in
   otherwise empty lines. Comments can be indented.  When
   *inline_comment_prefixes* is given, it will be used as the set of
   substrings that prefix comments in non-empty lines.

   When *strict* is "True" (the default), the parser won't allow for
   any section or option duplicates while reading from a single source
   (file, string or dictionary), raising "DuplicateSectionError" or
   "DuplicateOptionError".  When *empty_lines_in_values* is "False"
   (default: "True"), each empty line marks the end of an option.
   Otherwise, internal empty lines of a multiline option are kept as
   part of the value. When *allow_no_value* is "True" (default:
   "False"), options without values are accepted; the value held for
   these is "None" and they are serialized without the trailing
   delimiter.

   When *default_section* is given, it specifies the name for the
   special section holding default values for other sections and
   interpolation purposes (normally named ""DEFAULT"").  This value
   can be retrieved and changed on runtime using the "default_section"
   instance attribute.

   Interpolation behaviour may be customized by providing a custom
   handler through the *interpolation* argument. "None" can be used to
   turn off interpolation completely, "ExtendedInterpolation()"
   provides a more advanced variant inspired by "zc.buildout".  More
   on the subject in the dedicated documentation section.

   All option names used in interpolation will be passed through the
   "optionxform()" method just like any other option name reference.
   For example, using the default implementation of "optionxform()"
   (which converts option names to lower case), the values "foo
   %(bar)s" and "foo %(BAR)s" are equivalent.

   When *converters* is given, it should be a dictionary where each
   key represents the name of a type converter and each value is a
   callable implementing the conversion from string to the desired
   datatype.  Every converter gets its own corresponding "get*()"
   method on the parser object and section proxies.

   在 3.1 版更改: The default *dict_type* is
   "collections.OrderedDict".

   在 3.2 版更改: *allow_no_value*, *delimiters*, *comment_prefixes*,
   *strict*, *empty_lines_in_values*, *default_section* and
   *interpolation* were added.

   在 3.5 版更改: The *converters* argument was added.

   defaults()

      Return a dictionary containing the instance-wide defaults.

   sections()

      Return a list of the sections available; the *default section*
      is not included in the list.

   add_section(section)

      Add a section named *section* to the instance.  If a section by
      the given name already exists, "DuplicateSectionError" is
      raised.  If the *default section* name is passed, "ValueError"
      is raised.  The name of the section must be a string; if not,
      "TypeError" is raised.

      在 3.2 版更改: Non-string section names raise "TypeError".

   has_section(section)

      Indicates whether the named *section* is present in the
      configuration. The *default section* is not acknowledged.

   options(section)

      Return a list of options available in the specified *section*.

   has_option(section, option)

      If the given *section* exists, and contains the given *option*,
      return "True"; otherwise return "False".  If the specified
      *section* is "None" or an empty string, DEFAULT is assumed.

   read(filenames, encoding=None)

      Attempt to read and parse an iterable of filenames, returning a
      list of filenames which were successfully parsed.

      If *filenames* is a string or *path-like object*, it is treated
      as a single filename.  If a file named in *filenames* cannot be
      opened, that file will be ignored.  This is designed so that you
      can specify an iterable of potential configuration file
      locations (for example, the current directory, the user's home
      directory, and some system-wide directory), and all existing
      configuration files in the iterable will be read.

      If none of the named files exist, the "ConfigParser" instance
      will contain an empty dataset.  An application which requires
      initial values to be loaded from a file should load the required
      file or files using "read_file()" before calling "read()" for
      any optional files:

         import configparser, os

         config = configparser.ConfigParser()
         config.read_file(open('defaults.cfg'))
         config.read(['site.cfg', os.path.expanduser('~/.myapp.cfg')],
                     encoding='cp1250')

      3.2 新版功能: The *encoding* parameter.  Previously, all files
      were read using the default encoding for "open()".

      3.6.1 新版功能: The *filenames* parameter accepts a *path-like
      object*.

   read_file(f, source=None)

      Read and parse configuration data from *f* which must be an
      iterable yielding Unicode strings (for example files opened in
      text mode).

      Optional argument *source* specifies the name of the file being
      read.  If not given and *f* has a "name" attribute, that is used
      for *source*; the default is "'<???>'".

      3.2 新版功能: Replaces "readfp()".

   read_string(string, source='<string>')

      Parse configuration data from a string.

      Optional argument *source* specifies a context-specific name of
      the string passed.  If not given, "'<string>'" is used.  This
      should commonly be a filesystem path or a URL.

      3.2 新版功能.

   read_dict(dictionary, source='<dict>')

      Load configuration from any object that provides a dict-like
      "items()" method.  Keys are section names, values are
      dictionaries with keys and values that should be present in the
      section.  If the used dictionary type preserves order, sections
      and their keys will be added in order. Values are automatically
      converted to strings.

      Optional argument *source* specifies a context-specific name of
      the dictionary passed.  If not given, "<dict>" is used.

      This method can be used to copy state between parsers.

      3.2 新版功能.

   get(section, option, *, raw=False, vars=None[, fallback])

      Get an *option* value for the named *section*.  If *vars* is
      provided, it must be a dictionary.  The *option* is looked up in
      *vars* (if provided), *section*, and in *DEFAULTSECT* in that
      order.  If the key is not found and *fallback* is provided, it
      is used as a fallback value.  "None" can be provided as a
      *fallback* value.

      All the "'%'" interpolations are expanded in the return values,
      unless the *raw* argument is true.  Values for interpolation
      keys are looked up in the same manner as the option.

      在 3.2 版更改: Arguments *raw*, *vars* and *fallback* are
      keyword only to protect users from trying to use the third
      argument as the *fallback* fallback (especially when using the
      mapping protocol).

   getint(section, option, *, raw=False, vars=None[, fallback])

      A convenience method which coerces the *option* in the specified
      *section* to an integer.  See "get()" for explanation of *raw*,
      *vars* and *fallback*.

   getfloat(section, option, *, raw=False, vars=None[, fallback])

      A convenience method which coerces the *option* in the specified
      *section* to a floating point number.  See "get()" for
      explanation of *raw*, *vars* and *fallback*.

   getboolean(section, option, *, raw=False, vars=None[, fallback])

      A convenience method which coerces the *option* in the specified
      *section* to a Boolean value.  Note that the accepted values for
      the option are "'1'", "'yes'", "'true'", and "'on'", which cause
      this method to return "True", and "'0'", "'no'", "'false'", and
      "'off'", which cause it to return "False".  These string values
      are checked in a case-insensitive manner.  Any other value will
      cause it to raise "ValueError".  See "get()" for explanation of
      *raw*, *vars* and *fallback*.

   items(raw=False, vars=None)
   items(section, raw=False, vars=None)

      When *section* is not given, return a list of *section_name*,
      *section_proxy* pairs, including DEFAULTSECT.

      Otherwise, return a list of *name*, *value* pairs for the
      options in the given *section*.  Optional arguments have the
      same meaning as for the "get()" method.

   set(section, option, value)

      If the given section exists, set the given option to the
      specified value; otherwise raise "NoSectionError".  *option* and
      *value* must be strings; if not, "TypeError" is raised.

   write(fileobject, space_around_delimiters=True)

      Write a representation of the configuration to the specified
      *file object*, which must be opened in text mode (accepting
      strings).  This representation can be parsed by a future
      "read()" call.  If *space_around_delimiters* is true, delimiters
      between keys and values are surrounded by spaces.

   remove_option(section, option)

      Remove the specified *option* from the specified *section*.  If
      the section does not exist, raise "NoSectionError".  If the
      option existed to be removed, return "True"; otherwise return
      "False".

   remove_section(section)

      Remove the specified *section* from the configuration.  If the
      section in fact existed, return "True".  Otherwise return
      "False".

   optionxform(option)

      Transforms the option name *option* as found in an input file or
      as passed in by client code to the form that should be used in
      the internal structures.  The default implementation returns a
      lower-case version of *option*; subclasses may override this or
      client code can set an attribute of this name on instances to
      affect this behavior.

      You don't need to subclass the parser to use this method, you
      can also set it on an instance, to a function that takes a
      string argument and returns a string.  Setting it to "str", for
      example, would make option names case sensitive:

         cfgparser = ConfigParser()
         cfgparser.optionxform = str

      Note that when reading configuration files, whitespace around
      the option names is stripped before "optionxform()" is called.

   readfp(fp, filename=None)

      3.2 版后已移除: Use "read_file()" instead.

      在 3.2 版更改: "readfp()" now iterates on *fp* instead of
      calling "fp.readline()".

      For existing code calling "readfp()" with arguments which don't
      support iteration, the following generator may be used as a
      wrapper around the file-like object:

         def readline_generator(fp):
             line = fp.readline()
             while line:
                 yield line
                 line = fp.readline()

      Instead of "parser.readfp(fp)" use
      "parser.read_file(readline_generator(fp))".

configparser.MAX_INTERPOLATION_DEPTH

   The maximum depth for recursive interpolation for "get()" when the
   *raw* parameter is false.  This is relevant only when the default
   *interpolation* is used.


14.2.10. RawConfigParser Objects
================================

class configparser.RawConfigParser(defaults=None, dict_type=collections.OrderedDict, allow_no_value=False, *, delimiters=('=', ':'), comment_prefixes=('#', ';'), inline_comment_prefixes=None, strict=True, empty_lines_in_values=True, default_section=configparser.DEFAULTSECT[, interpolation])

   Legacy variant of the "ConfigParser" with interpolation disabled by
   default and unsafe "add_section" and "set" methods.

   注解: Consider using "ConfigParser" instead which checks types of
     the values to be stored internally.  If you don't want
     interpolation, you can use "ConfigParser(interpolation=None)".

   add_section(section)

      Add a section named *section* to the instance.  If a section by
      the given name already exists, "DuplicateSectionError" is
      raised.  If the *default section* name is passed, "ValueError"
      is raised.

      Type of *section* is not checked which lets users create non-
      string named sections.  This behaviour is unsupported and may
      cause internal errors.

   set(section, option, value)

      If the given section exists, set the given option to the
      specified value; otherwise raise "NoSectionError".  While it is
      possible to use "RawConfigParser" (or "ConfigParser" with *raw*
      parameters set to true) for *internal* storage of non-string
      values, full functionality (including interpolation and output
      to files) can only be achieved using string values.

      This method lets users assign non-string values to keys
      internally.  This behaviour is unsupported and will cause errors
      when attempting to write to a file or get it in non-raw mode.
      **Use the mapping protocol API** which does not allow such
      assignments to take place.


14.2.11. 异常
=============

exception configparser.Error

   Base class for all other "configparser" exceptions.

exception configparser.NoSectionError

   Exception raised when a specified section is not found.

exception configparser.DuplicateSectionError

   Exception raised if "add_section()" is called with the name of a
   section that is already present or in strict parsers when a section
   if found more than once in a single input file, string or
   dictionary.

   3.2 新版功能: Optional "source" and "lineno" attributes and
   arguments to "__init__()" were added.

exception configparser.DuplicateOptionError

   Exception raised by strict parsers if a single option appears twice
   during reading from a single file, string or dictionary. This
   catches misspellings and case sensitivity-related errors, e.g. a
   dictionary may have two keys representing the same case-insensitive
   configuration key.

exception configparser.NoOptionError

   Exception raised when a specified option is not found in the
   specified section.

exception configparser.InterpolationError

   Base class for exceptions raised when problems occur performing
   string interpolation.

exception configparser.InterpolationDepthError

   Exception raised when string interpolation cannot be completed
   because the number of iterations exceeds "MAX_INTERPOLATION_DEPTH".
   Subclass of "InterpolationError".

exception configparser.InterpolationMissingOptionError

   Exception raised when an option referenced from a value does not
   exist. Subclass of "InterpolationError".

exception configparser.InterpolationSyntaxError

   Exception raised when the source text into which substitutions are
   made does not conform to the required syntax.  Subclass of
   "InterpolationError".

exception configparser.MissingSectionHeaderError

   Exception raised when attempting to parse a file which has no
   section headers.

exception configparser.ParsingError

   Exception raised when errors occur attempting to parse a file.

   在 3.2 版更改: The "filename" attribute and "__init__()" argument
   were renamed to "source" for consistency.

-[ 脚注 ]-

[1] Config parsers allow for heavy customization.  If you are
    interested in changing the behaviour outlined by the footnote
    reference, consult the Customizing Parser Behaviour section.
